This invention relates generally to the field of ink jet printers and more particularly to an ink supply system for supplying ink from an ink reservoir to a piezoelectrically operated printing jet employed in ink jet printers.
Generally, in ink jet printers using piezoelectrically operated printing jets, the printing liquid (usually ink) is drawn from a reservoir and supplied to a printing jet. Typically, the printing jet comprises a thin walled hollow tube surrounded by a tubular piezoelectric transducer which contracts upon excitation by a voltage pulse. A resultant pressure wave forces a drop of ink to issue from the orifice of the printing jet. Depending upon the type of system used, printing is carried out either by several printing jets (as are used in mosaic printers), so that the ink droplets impact directly upon the data carrier, or by using only a single printing jet, the ink droplets issuing therefrom being charged by a strong electric field, accelerated and deflected by a deflector device in accordance with the cycle of operation of a character generator, as will be understood by those skilled in the art.
In order to provide an undisturbed printing operation it is necessary to prevent fluctuations in the compressibility of the liquid (ink) enclosed within the printing jet, which may arise by virtue of the entrapment of air in the liquid. Such trapped air (in the form of small bubbles) or possibly other foreign bodies contained within the printing liquid may result in failure of the printing jet. The undesirable gas can penetrate into the printing jet in two ways, either in the form of air bubbles entrained within the liquid or by ingress through the jet orifice when the printing jet is vibrated.
Ink jet printers are known in which ink is supplied to a printing jet from an ink tank through an ink duct, and expelled from the printing jet to effect printing. Such known jet printers may include a mechanism for removing air entrained within the ink, consisting of an intermediate vessel connected to a first ink duct, through which ink is supplied to the vessel. The vessel itself comprises an upwardly flaring or expanding portion, and to the base of the vessel is connected a second duct, through which ink is supplied to the printing jet. By alternately opening and closing a valving arrangement associated with the ink lines, and in combination with an air receiver, the air contained in the ink can be removed.
Also known in connection with such jet printers is an ink reservoir comprising a flexible ink bag for receiving the ink, which bag comprises, at the upper portion thereof, an ink-filter distributor in which an air bubble is entrapped for regulating the pressure fluctuations within the distributor. The air bubbles entrained within the ink are collected in the upper portion and can be vented through the cover of the distributor.
Such known systems for removing entrained air and attenuating pressure waves and variations are somewhat complicated and consequently relatively expensive in manufacture.